1. Field of the Invention
This invention relates generally to a water purifying unit incorporating a filter, and more particularly to an electronic controller for a water purifying unit for providing monitoring and test functions for indicating, for example, when the filter should be replaced.
2. Description of the Prior Art
With ever-increasing population and industrialization, the quality of the water supply for use in the home and work place is believed to have deteriorated, even though chemicals such as chlorine and the like, have been added to the water to improve it. Accordingly, a need exists worldwide for an economical water purification system for use in the home and work place to improve the quality of tap water for drinking, cooking, ice-making and the like. A need further exists for an electronic controller for such a water purification system for providing monitoring and test functions; the electronic controller being of simple design and low power consumption.
Some typical prior art water purification systems include, in addition to a filter in the form of a reverse osmosis membrane, a pre-filter for initial screening of the feed or tap water to protect the membrane from clogging, and a post-filter for further purification, especially for the removal of organics such as dissolved hydrocarbons. In general, in these systems, the tap or feed water is filtered and separated into purified water and waste water. Since the filters constitute a major restriction in the water purification system, the filtration process is relatively slow. Therefore, a system of a size which is economically and esthetically practical for the home and the work place is generally not able to generate adequate amounts of water on demand, but must include a water storage reservoir.
Over a period of time, the reverse osmosis membrane or filter will become less effective due to the formation of precipitates, scale, or particulate matter on the inlet side of the membrane. If this condition is not detected and corrected by replacement of the filter, the water purification unit becomes inefficient, and the quality of purification drops. Accordingly, a strong need exists in the industry for an electronic controller for a water purification unit which detects, among other things, when the filter should be replaced, whether there is tap water pressure in the unit, and whether the water storage reservoir is being filled.
The prior art, relative to water purification systems, includes U.S. Pat. No. 3,838,774, which issued to Dolan et al. This patent discloses an apparatus for monitoring water purification systems. The system typically includes an inlet chamber for receiving tap water, an outlet chamber for receiving purified water, and a membrane separating the inlet and outlet chambers for filtering the tap water as it passes from the inlet chamber to the outlet chamber. A conductivity sensing probe, operatively associated with the inlet side, senses the electrical conductivity of the tap water. A similar sensing probe, associated with the outlet side, senses the electrical conductivity of the purified water. The conductivity sensing probes are powered by an electrical source and a develop output signals that are compared against a known threshold. The output comparison is also viewable on a meter, recorder, and/or alarm device to continuously indicate the effectiveness of the filtering system.
In accordance with a specific embodiment of the invention of U.S. Pat. No. 3,838,774, the conductivity sensing probe on the inlet side is connected in the negative feedback path of an operational type amplifier and the conductivity sensing probe on the outlet side is connected across the negative and positive inputs of the amplifier. In accordance with these connections the output voltage of the amplifier is proportional to the ratio of the conductivity of the purified water to the conductivity of the tap water; which ratio, in turn, is a continuous measure of the relative impurity levels.
A serious disadvantage of the continuously-monitoring type systems disclosed in the prior art is that the power consumption for operating such systems is extremely high. Where batteries are used as the power supply, the high continuous current drain of such systems would soon drain the battery, requiring battery replacement, or a costly battery charging system to keep the battery fully charged.
A further disadvantage of the prior art systems is the lack of a straightforward means to compensate for the inevitable differences in probe calibration factors which may vary because of design, material and/or manufacturing differences.